Electrodynamic receiver



Mar. 13, 1923. 1,448,279

E. S. PRIDHAM ET AL ELECTRODYNAMIC RECEIVER Filed Apr. 28, 1920 2 sheets-sheet l 1N VENTORS 50m 5. HPIDIZIM PETER L. JENSEN ,4 TTORNE Y Mar. 13, 1923.

E. S. PRIDHAM ET AL ELECTRODYNAMIC RECEIVER Filed Apr. 28, 1920 IN V EN TORS EDWIN 6. PlPlDflfi/I PETE/F L. JEA/5EN A TTOR NE Y Patented Mar. 13, 1923.

UNITE EDWIN S. rmnmm AND PETER L. JENSEN, OF OAKLAND,

camroama, asS IGNOns TO MAGNAVOX COMPANY, 013' OAKLAND, CALIFORNIA, A CORPORATION OF ARI- ZONA.

ELECTEODYNAJIIC RECEIVER.

Application filed April 28, 1820. Serial 80. 87?,354.

To all whom it may comer:

Be it known that we, EDWIN S. PRIDIIAM and PETER L. JENSEN, citizens of the United States, residing at Oakland, in the county of Alameda and State of California, have invented a new and useful Improvement in Electrodynamic Receivers, of which .the following is a specification.

This invention relates to telephones and more specifically to improvements in the moving coil type of telephone receivers. The receiving instrument which is the subject of this specification comprises an annular coil rigidly connected to the diaphragm. This coil is disposed, so as to be freely movable, in a strong concentric magnetic field produced either by a permanent or an electromagnet. The magnetic field is so arranged that the linesof force out the annular coil at all points in the same direction.

This is accomplished by lhavin one of the poles of the magnet within it e coil and the other completely surrounding it.

In the accompanying drawings, we have shown two devices of magnetizing structure, namely permanent magnet and an electroma et. a

ig. 1-shows a plan vview of the device using an electrom'a'gnet *as the magnetizing structure.

Fi 2 shows a vertical cross-section of the evice shown in Fig. .1.

Fig. 3 shows an enlarged detail sectional view of a portion of the device shown in fiig. 4 shows a vertical cross-section of the device in modified form using a permanent ma et as the magnetizin' structure.

ig. 5 is a diagram showing the electrical connections for the receiver.

Referring now in detail to the drawings, 2 is the sound box, 3 the diaphragm, 4 an insulator frame with a trough or depression cut into it and forming an annular oove in which the coil 5 is fixed. This insulator frame 4 is rigidly attached to the diaphragm by means of the bracket support 6 and is held in place on the diaphragm by the screw 7 and lock nut 8. The pole piece 9 is provided with a circular hole of sufficiently great diameter to admit the coil 5'with a few thousandths of an inch clearance. Rigidly attached to the pole piece 9 spacing ring 11 by means of set screws The assembly is then a unit and can be placed on any. magnetizing structure designed for it.

In F ig. 4, we have shown the assembly adapted to be used with a permanent magnet. In this case, the inner pole piece 12 is fixed to an extension 12 of one'of the oles The pole piece 9 is fixed to the po c N of a permanent magnet. The sound box with the diaphragm and coil are fixed in relation to the pole piece 9 and may be removed as a unit from the structure.

In Fig. 1 we have shown the receiver head assembly which is the name given to the sound box diaphragm, coil and upper pole piece, adapted to be placed upon an electromagnetic structure. The electromagnetic structure consists of an iron cylinder 14, and iron base 15. The magnetizing coil '16 wound on the core 17 is placed within the iron cylinder to form a substantially closed magnetic circuit when the pole pieces 9 and 12 are in position. The iron core 17 of the magnetizing coil 16 is bored out to form a seat for the pole piece 12 so as to make a good magnetic contact. It will be seen that the receiver head can be assembled as a unit apart from the magnetizing structure and can be placed on or removed from any magnetizing structure adapted to receive it.

We have found that the greater the den- I so as to utilize to the highestdegree the magnetic flux of the magnetic structure. For

this reason it will be apparent that the cross section of the air gap must not be greater than the cross section of the central p ole. Thus the depth of the airgap for maximum elficiency cannot be more than one quarter of the diameter of the central pole, as the area of the cylinder equalsthe cross section of tened to the spacing ring. Thus we have a unit assembly of sound box with its diaphragm and coil, outer pole piece and: inner pole piece all in correct relation and ready to. be mounted on the magnetizing structure.

We have made certain mechanical improve merits in the receiver which have aided greatly in the construction of the instrument. As mentioned above, the flux density should be as great as possible so for this reason the width of the airgap should be kept a minimum just suficient to admit the moving an-' nular coil with a few thousandths of an inch clearance on either side. With such a small clearance it is important that the innor pole be Mcurately spaced in relation to the surrounding pole. Wehave also found it to be advantageous to construct the inner and outer pole as a unit with the soundbox and movab e coil so that they can be placed or removed as a unit on the magnetizing structure. In this way a receiver head or unit as the assembly of inner and outer pole pieces with the sound box and movable coil is termed can be fitted to any magnetizing structure (such as a permanent magnet or electromagnet) for which it has been designed.

The inner pole piece is rigidly held in fixed relation to the outer pole'piece by means of the spacing ring 11. When this spacing ring has been fixed in proper relationto the outer pole piece, its inner diameter is such that the inner pole piece is held in proper relation to the outer pole piece and the airgap is fixed. The inner pole piece is held rigidly in the spacing ring by means of set screws.'

The great advantage secured by this mechanism lies in the fact that the. sound box", with its diaphragm and coil can be mounted and fixed in position on the pole piece which surrounds thecoil, and then by 2 a the spacing ring on this surrounding polepiece, the inner core or pole piece is caused to position itself correctly in relatages, the movable coil is so deslgned that tion to the movable coil:

This receiver has several unique advanits altitude is substantiallyone quarter the diameter of the inside pole piece 12, thereby taking advantage "0t: themaximum number of lines ct force a in the or pole ianaare piece at the maxim density... The construction is such as to permit ease of assemhim and ad usting and ing the relation of t epole ieces to the movable coil. it permits of exibihty in manufacturing op.-

erations, as the receiver head and the magnctizing structure'may be completed. independently and then assembled to form the com lete unit.

T e advantages secured by this construction are very evident. The sound box with its diaphragm and coil can be mounted in fixed relation with the upper pole piece 9. The spacing ring is then adjusted and fixed on the polepiieceil by means of the set screw 10-10, so at therewill be'unit'orm clearance between thepole piece 12 and the. frame a, when this pole piece 12 is put in placein the ring 11. The set screws 1313 are then tightened to prevent any movement of the pole piece 12.

The electrical connections for the receiver are shown in Fig. 5 and include an operating circuit 18 for themagnetizing coil 16. A transmitter 19 having an operating circuit 20 is also shown. llncluded in this operating circuit is the primary of. an induction coil 21, the secondary of which is connected electrically with the vibrating coil 5.. Having thus described our invention, what out is:

and a receiver head assembly to -fit over the we claim and desire to secure by Letters Pat- 1. In an electro-dynamicreceiver a casing,

, a magnetizing structure within .the casing 1 00 casing, said assembly includin a'sound boxried by the spacing ring, said pole pieces being arranged to co-operate with the mag-' netic structure within the casing.

. 2. A receiver head assembly comprising an outer pole piece, a sound box including a diaphragm mounted upon and connected to said pole piece, an annular coil fixed to i said diaphra and extending into a central opening in said pole piece, an mner pole piece extending within the annular coil and spaced therefrom, a spacing ring connected tothe outer pole piece and supporting the inner pole piece, the foregoing parts forming one unit of an electro-dynamic receiver and a magnetizing structure forming a separate unit with which said pole pieces'cooperate.

3. In a telephone of the moving coil type, a sound box including a diaphragm, an annular coil rigidly attached to said diaphragm, a circumferential pole piece surrounding said coil and spaced therefrom, a spacing ring detachably mounted on said circumfere'ntial pole piece and supported thereby, and an or pole piece detachably mounted in said spacing ring, said inner p'ole piece extending withm the annular coil and spaced therefrom. 4. In a telephone receiver of the moving coil type, a magnetizing structure, a receiver head or operating structure adapted to be, placed upon or removed from said magnetizing structure as a unit .said receiver head comprising a circumferential pole piece, a

sound box supported upon said circumferem tial pole iece, a diaphragm on the sound box, a coil on the diaphragm extending into a central opening formed in the circumfer ential pole piece said coil being surrounded by said circumferential pole piece, a specing ring mounted upon said pole piece, and an inner pole held in position by said s acing ring and extending within but free f om said annular coil, said receiver head andsaid magnetizing structure adapted to fit toether to form a working magnetic circuit or the. purposes as set forth.

5. In an electrodynamic telephone receiver, a receiver head comprising as a unit ing a base of insulating material, a shell or assembly a sound 'box including a diaphragm, an annular movable coil rigidly fixed to said diaphragm, a pole piece completely surrounding said coil but free from it, a spacing ring mounted upon said pole piece, a second pole piece held in said spac-;

ing ring and extending within but free from,

said annular coil, means for connecting said coil to a telephone circuit, in combination with a magnetizing circuit, said magnetizing circuit comprising a unit assembly as follows, a casmg having a base, said caslng and base being of magnetic material, an energizing coil having an iron core contained within said casing, said iron core being fastened at one end to the base of the easing, the other'end of said iron core being bored out to form a seat for said second pole piece of said receiver head, and connections to said energizing coil for the passing of the magnetizing current. 4

6. In an electro-dynamic receiver, the combination of inner and outer pole pieces having a circumferential air gap between them, an annular coil arranged in said air gap, said coil includin an insulator frame carrying a large num r of turns of fine wire a sound box including a flexible dia phragm and means for rigidly connecting said coil and diaphragm, said means including a conical open-sided member connected at its apex to the diaphragm and at its base to the insulator frame.

7. In an electro-dynamic receiver, the combination of inner and outer pole pieces having a circumferential air gap between them, an annular coil arranged in said air gap. said coil including an insulator frame having a depression cut therein and a large number of turns of fine wire. arranged in 'the casing to the top thereof and formed .'a diaphragm and a movable coil rigidly and formed at its upper end with an inner said depression, a sound box carrying a fiexible diaphra and arms extending up from said insulating frame to the diaphragm for rigidly connecting said annular coil to the diaphragm.

8. An electro-dynamic receiver comprising a shell or casing having bottom and side walls formed. of magnetizablc material, a magnet zing coil within said casing, a core for the coil extending fromthe bottom of at its upper end with an inner pole piece,, an outer pole piece in the form of a flat plate arranged upon the casing and having a central opening surrounding the inner pole piece and spaced evenly therefrom, means within the casing for retaining said pole pieces in spaced relation, a sound box carried by the casing, said sound box including connected to the diaphragm and arranged within the space between the two pole pieces. a

9. An electro-dynamic receiver compriscasing having bottom and side walls of-magnetizable material arranged upon the base, a magnetizing coil'within the casing, a core for said coil contacting with the bottom of the casing and extending to the top thereof 9 pole piece, an outer pole piece formed with a flat plate arranged upon the casing. and

having an opening surrounding the inner pole piece and spaced evenly therefrom, means within the casing for retaining said pole pieces in spaced relation, a sound box carried by the casing. said sound box including a diaphragm and a movable coil rigidly. connectedto the diaphragmand arranged within the space between the two pole pieces.

10. An electro-dynamic receiver comprising a shell or casing having bottom and side walls formed of magnetizable material, a magnetizing coil within the casing, a core for said coil having contact at its lower end with the bottom of the casing, an extension on the upper end of the core forming an inner pole piece, an outer pole piece in the form of a plate removably mounted on the casing, said outer pole piece having an opening spaced cir'cumferentially from the inner pole piece, means within the casing for retaining the pole pieces in spaced relation, a sound box arranged upon the outer pole piece and supported thereon, said sound box including a diaphragm and an annular coil rigidly connected to the diaphragm and arranged within the space between the'two pole pieces.

In testimony whereof we have hereunto set our hands. I v'EIIWVIN S. PRIDHAM.

PETER JENSEN. 

